Abstract 1004: LDLR knockdown reduces the growth of Her2 overexpressing breast cancer in mouse models of hyperlipidemia

Abstract

Abstract Women with higher circulating low density lipoprotein (LDL) cholesterol levels are more likely to have advanced HER2 positive breast cancers. The LDL receptor (LDLR) is the main receptor for cholesterol uptake into cells from circulating LDL and its expression is higher in HER2 positive breast cancers than other subtypes. The aim of our study was to understand the importance of the LDLR in the progression of HER2 positive breast cancer growth in the setting of hyperlipidemia. To study the role of hyperlipidemia in HER2 cancer progression, we used two mouse models with elevated LDL cholesterol: Apolipoprotein E knockout (ApoE-/-), and LDLR knockout (LDLR-/-) mice on an FVB/n background. ApoE-/-, LDLR-/- and control (WT) mice were placed on a western diet at 8-10 weeks of age. After 2 weeks on the diet, serum cholesterol concentrations were measured and demonstrated significantly higher cholesterol levels in the ApoE-/- and LDLR-/- mice compared with WT mice (WT: 208±19mg/dL; LDLR-/-: 488±37mg/dL; ApoE-/- 660±39mg/dL). We used the MCNeuA (MMTV-Neu derived) breast cancer cells to study the effect of hyperlipidemia on Her2/Neu positive breast cancer in this model, as the MCNeuA cells were found to have high levels of LDLR protein expression compared with other murine breast cancer cell lines. To study the importance of the LDLR in mediating the effects of hyperlipidemia, we knocked down the LDLR in the MCNeuA cells using shRNA, and selected two cell clones with successful gene knockdown confirmed by RNA and protein analysis. ApoE-/-, LDLR-/- and WT mice on the western diet were injected into the 4th mammary fat pad with 2 x 106 MCNeuA (MMTV-Neu derived) control shRNA or MCNeuA LDLR knockdown clone 1 or clone 2 cells (n=6-10 mice per group). Tumor growth was measured for 30 days. Control shRNA tumors in both hyperlipidemic mouse genotypes grew more rapidly than in the WT mice. 30 days after injection the control tumor volumes were: WT 514±66.5mm3; LDLR-/- 767±78.2mm3; ApoE-/- 1189±94mm3. The LDLR knockdown clones 1 and 2 had a reduction of tumor volume of 11% and 30% in the WT mice, 28% and 62% in LDLR-/- mice, and 26% and 53% in the ApoE-/- mice, respectively compared with the control shRNA cells. Western blot analysis of tumor protein lysates showed an increase in p19 cleaved caspase 3 in the tumors with LDLR knockdown, compared with the control cells. In vitro studies demonstrated a decrease in survival of MCNeuA cells with LDLR knockdown in serum starved conditions, and an increase in caspase 3 cleavage. These data demonstrate that hyperlipidemia promotes the growth of Her2/Neu overexpressing breast cancer cells and the LDLR plays an important role in protecting Her2 / Neu tumors from apoptosis. Therefore, targeting cholesterol uptake and metabolism may be an important strategy for women with HER2 positive breast cancers. Citation Format: Emily J. Gallagher, Brian A. Neel, Zara Zelenko, Irini Markella Antoniou, Nathan Kase, Derek LeRoith. LDLR knockdown reduces the growth of Her2 overexpressing breast cancer in mouse models of hyperlipidemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1004. doi:10.1158/1538-7445.AM2017-1004